The molecule 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS) is an important redox-active compound with broad chemical, material and biomedical applications. For example, ABTS and its derivatives have been used as the electrochromic component in smart windows,1 as a chromogenic substrate in assays for enzymatic activity2 and as a mediator for electron transfer in bioelectrocatalysis.3 Interest in the use of ABTS in the bioelectrocatalytic reduction of oxygen to water has increased primarily because its redox potential is near that of oxygen under mildly acidic conditions.4 